Evaluation of Time-Dependent Deformation Behavior of Pharmaceutical Excipients in the Tableting Process

Tableting is a critical process in the manufacture of pharmaceutical tablets that directly influences product quality. Ensuring consistent quality between the research and development phase and commercial-scale production is essential during scale-up. In this study, we investigated methods for evaluating time-dependent deformation behavior using four excipients that exhibit different compression deformation behaviors. Dicalcium phosphate dihydrate (DCPD) shows no viscoelasticity, whereas lactose monohydrate (LAC), cornstarch (CS), and microcrystalline cellulose (MCC) exhibit viscoelasticity and viscoplasticity, although the degree of viscosity varies between them. In addition to investigating the known strain rate sensitivity (SRS), we performed mechanical energy evaluation based on the area under the force-displacement curve and stress relaxation tests. A trapezoid waveform was applied during the test, with loading punch speeds of 0.5 and 100 mm/s, and a dwell time of 4.5 s. The SRS value for DCPD approached approximately one, indicating no speed dependence, and the SRS increased in the order of LAC < MCC < CS, consistent with previous studies that used a saw-tooth waveform. Among the mechanical energies, the ratio of plastic flow energy to plastic energy, which depends on dwell time, followed a similar trend to SRS for the three materials other than DCPD. We conclude that axial stress relaxation is affected by machine deformation, whereas radial stress relaxation provides insight into the viscous behavior of the material. Under the test conditions, the effects of the punch-displacement profile and compression pressure on the mechanical energy and stress relaxation were more pronounced than those of SRS.